Device for closing a pot-like digestion vessel

ABSTRACT

A device  5  for closing pot-like digestion vessel  1  whose opening is covered by a cover  3,  has a pressure-applying plunger  6,  a screwing part  7  arranged co-axially with the pressure applying plunger  6  and a resilient pressure-generating means  8  arranged between the pressure-applying plunger  6  and the screwing part. The screwing part and the pressure-applying plunger  6  fit round one another in a socketed arrangement.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a device for closing a pot-like digestion vessel for the analysis of heated materials.

[0003] To perform an analysis of materials, it is known for one or more materials, e.g. a solid or liquid sample material, to be heated in a digestion vessel, as a result of which a pressure above atmospheric is generated in the digestion vessel and this in turn promotes the digestion of the sample material.

[0004] A device of this kind is described in EP 0 830 891 A1. In this generic design a resilient pressure-generating means which acts between a screwing part and a pressure-applying plunger is formed by a stack of metal disc springs arranged one above the other, the pressure-applying plunger taking the form of a U-shaped component in which is arranged a dome-like cage part which is of metal and forms a Faraday cage for the disc springs. This device has a large number of parts and is structurally large and in particular tall, which means that it too has the advantages described above.

[0005] A device for closing a pot-like digestion vessel is also described in GB 2 184 040 A. In this known device, the pressure-applying plunger, the screwing part, and the resilient pressure-generating means arranged between them, are held in a hat-like screwed cover of a pot-like supporting vessel, into which is fitted a holding vessel against whose cover the pressure-applying plunger acts. The screwing part is mounted to be vertically displaceable on a pressure-applying piece in a vertical guide hole in the screwed cover and is in the form of a nut which is screwed onto a pressure-applying piece, which latter extends co-axially upwards from the pressure-applying plunger and is on a threaded stem which passes through a guide hole. In the annular wall of the hat-like screwed cover there is arranged, at the same height as the top edge of the supporting vessel in the screwed-on state, an internal annular groove from which a venting passage extends radially outwards through the annular wall. This known design has a large number of parts, is structurally large, is complicated and costly to manufacture and is time-consuming to manipulate. There is also the risk that the pressure-applying piece and the nut will move away from one another, due to fouling for example, as a result of which different pressure ranges will arise when the cover of the holding vessel is closed and opened.

SUMMARY OF THE INVENTION

[0006] The object of the invention is to simplify a device of the kind detailed at the beginning and to design it in such a way that a small or low construction is obtained. Furthermore, the device is to be improved in respect of its operation. An attempt is also made to reduce the number of separate parts in the device and the amount of material it consumes.

[0007] In a device according to the invention, a pressure-applying plunger and a screwing part fit around one another in a socketed arrangement.

[0008] In more specific aspects, at least one annular wall, which may be part of the pressure-applying plunger and which extends upwards therefrom preferably as an integral part thereof, fits around the screwing part like a socket. Also, the annular wall may be part of the screwing part and may extend downwardly therefrom, preferably as an integral part thereof and may fit around the pressure-applying plunger like a socket.

[0009] In other specific aspects, two circumferential walls are provided of which extends upwardly from the pressure-applying plunger and the other extends downwardly from the screwing part wherein one of the annular walls fits around the other in a socketed arrangement. Not only does this allow guidance and/or radial support to be obtained for the pressure-applying plunger but the interior space between the pressure-applying plunger and the screwing part which holds the resilient pressure-generating means is closed off by at least one annular wall, which means that it is possible neither for contaminants from the holding space in the holding vessel to make their way out into the interior space for the resilient pressure-generating means if there is a reaction which produces an excess pressure and lifts the cover of the holding vessel, nor for other contaminants to do so from the surroundings of the device. The interior space is also protected against aggressive treating or digesting chemicals in this way, as a result of which the movement mechanism of the device is protected and a long life is obtained. If mounting is on a thread, this gives positive guidance in both axial directions of movement, and in the event of an adjustment this means that the screwing part will still be safely and securely adjusted when there is some tightness in the mounting.

[0010] According to a further aspect, the seal between the pressure-applying plunger and the screwing part can be improved by arranging between the guide faces which co-operate in a socketed arrangement a seal, and preferably a ring seal, which may for example be an O-ring, which can be inserted in an external annular groove in the part which is fitted round or in an internal annular groove in the part which fits round.

[0011] Within the scope of the invention there are many possible ways for the screwing part to be supported against an abutment. An abutment of this kind may for example be formed by a supported disc which fits round a location for the digestion vessel in a space to which microwaves can be applied. If a disc of this kind is open in all directions it can also be used to cover a plurality of circumferentially distributed locations for digestion vessels having the device. In this case the disc may, in a known manner, be a turntable which is mounted to be rotatable in the microwaving space together with the locations.

[0012] The abutment may also be formed by the top wall of a pressure-supporting body which defines the two sides, the top and the bottom of a location for a digestion vessel. In this embodiment the digestion vessel may be placed in the location and removed from it again from one side, with the device if required.

[0013] It is also possible in accordance with another aspect of the invention for the abutment to be formed on or supported against the circumferential surface of the digestion vessel. For this purpose the screwing part may be formed by the top wall of a cap whose annular wall can be connected, in the free area of its edge for example, to the digestion vessel, by screws for example. It is particularly advantageous in this case if an externally-threaded screwed ring is fitted onto the circumferential surface of the digestion vessel and is supported against the vessel, preferably against the underside of a flange in the edge region of the digestion vessel, so that the flange will provide the reaction forces from the device and will ensure the screwed ring is located by contact. This embodiment is notable for its small structure, which takes up little space, is handy, consumes little material and is also low in weight.

[0014] It is possible and advantageous in all the embodiments for a marking or scale to be so arranged between the screwing part or parts added thereto and the abutment that, in respect of the resilient closing force from the pressure-generating means, the screwing part can be preset in steps or steplessly in such a way that a given opening pressure is obtained at which, if it is exceeded in the interior space in the digestion vessel, the cover of the vessel automatically lifts and thus opens. This allows the operator to preset desired maximum internal pressures in the holding space in the holding vessel in the light of the material or materials to be treated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Advantageous embodiments of the invention will be explained in detail below by reference to a plurality of embodiments and drawings. In the drawings

[0016]FIG. 1 is a vertical section through a vessel arrangement having a device according to the invention for closing a digestion vessel;

[0017]FIG. 2 is an enlarged view of the detail marked X in FIG. 1; and

[0018]FIG. 3 is a vertical section through a modified vessel arrangement having a device for sealing a digestion vessel which is also modified.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A pot-like digestion vessel 1, having a circumferential wall 1 a which is in the form of a hollow cylinder and is for example relatively thin, and a flat bottom wall 1 b, is surrounded, and supported in the radially outward direction, by a supporting shell 2 in the form of a hollow cylinder which may extend up to a flange 1 c at the top edge of the circumferential wall 1 a, thus allowing the flange 1 c to rest on the top front face of the supporting shell 2.

[0020] The opening at the top of the digestion vessel 1 has to be opened and closed with a cover 3 which is for example flat and in the form of a stepped cylinder and of which, in the embodiment shown, a bottom cylindrical extension 3 a fits into the digestion vessel 1 with little play and is sealed, preferably by a ring seal 4. The latter may be formed by an O-ring 4 a which is mounted in an annular groove in the circumferential surface of the cover extension 3 a. The cover 3 thus rests on the flange 1 c by face 3 b of its shoulder.

[0021] The device for closing the digestion vessel 1 even when there is a pressure above atmospheric in the digestion space 1 d within the vessel, which device is referred to as a whole by reference numeral 5, comprises three main parts, namely a pressure-applying plunger 6, a screwing part 7 at least part of which is arranged over the latter, and a resilient pressure-generating means 8 which is arranged between an upwardly directed supporting face 6 a on the pressure-applying plunger 6 and a downwardly directed supporting face 7 a on the screwing part 7 and which in functional operation is preloaded with a given compressive force. In the embodiment shown the pressure-generating means 8 comprises a plurality of disc springs stacked on top of one another in opposite directions. At least in its upper region the screwing part 7 has an outside thread 7 b by which it is screwed into a threaded bore 9 a in an abutment 9 as a screwing part. To allow the screwing part 7 to be turned, there is arranged in its top face an element 11 for applying rotation intended for a tool for rotation which can be positively engaged therewith in rotation. In the embodiment shown the element 11 for applying rotation is formed by a non-circular recess for insertion.

[0022] To cover the space 12 occupied by the pressure-generating means and thus to protect it from fouling, there is provided an annular wall 7 c which surrounds the space 12 and which fits at least partly round the pressure-applying plunger 6 and/or the screwing part 7 in a socketed arrangement. In the embodiment shown the annular wall 7 c, which is preferably in the form of a hollow cylinder, extends downwards from the screwing part 7 as an integral part thereof, in which case it at least partly fits over the preferably cylindrical circumferential surface of the pressure-applying plunger 6 with clearance for movement, thus making space 12 inaccessible from the sides.

[0023] The amount of vertical overlap a may be sufficiently large to allow a guidance function to be performed between the pressure-applying plunger 6 and the screwing part 7 and/or a ring seal 13 when the device 5 telescopes in a manner which has yet to be described. Arranged in the gap at the overlap there is preferably a sealing ring 13 a, e.g. an O-ring, which is mounted in an annular groove in the circumferential surface of the pressure-applying plunger 6 and which is covered by the inner surface of the annular wall 7 c in any telescoped position. The maximum amount of telescoping movement b in the vertical direction is determined in the present embodiment by the distance between the annular wall 7 c and the cover 3. If the pressure-applying plunger 6 is formed to have a flange 6 b as indicated in ghost lines, then the maximum amount of telescoping movement b will be determined by the distance from flange 6 a. Flange 6 b allows the area over which the pressure-applying plunger 6 acts against the cover 3 to be enlarged and the pressure per unit area which comes into play in operation to be reduced.

[0024] The pressure-generating means 8 or rather the spring discs may be located by the inner circumferential surface of the annular wall 7 c. However, to reduce the frictional wear which occurs between the two during telescoping, the pressure-generating means 8, which is preferably annular, is located on the inside with a small amount of clearance for movement by a locating spigot 6 c which in the embodiment shown extends upward from the pressure-applying plunger 6 as an integral part thereof and may then engage in, or terminate shortly before, a guide hole 7 d present between supporting face 7 a and the element 11 for applying rotation, thus providing additional guidance, which is not absolutely essential however, for the pressure-applying plunger 6.

[0025] Arranged in the pressure-applying plunger 6, preferably co-axially therewith, is a full-length hole 14 which may for example be lined with an annular wall 15 which may have at the bottom end a flange which allows it to be inset into a recess in the pressure-applying face. To allow it to be secured axially in the pressure-applying plunger 6, the annular wall 15 may be a press-fit in the plunger.

[0026] The hole 14 may be used to hold functional members, e.g. sensor members, which pass through the screwing part 7 and which are functionally connected above it to associated control or regulating devices. A temperature sensor for example may be provided, which is inserted in hole 14. A pressure measuring element may also be inserted in hole 14, whose vertical position, or rather whose change in position, when the cover 3 lifts serves as an indication of the level of the internal pressure prevailing in the digestion space 1 d in operation.

[0027] In the embodiment shown in FIG. 1, the abutment 9 is formed by the top wall 16 a of a supporting housing 16 which may be of box-like configuration with a curved wall 16 b and two side walls 16 c and which forms a holding space 17 for the digestion vessel 1 which is open at the front or extends right through horizontally and in which the vessel can be set up from the appropriate side and from which it can be removed again. In the set-up state, the digestion vessel 1 stands with its bottom wall 1 b, which is flat in the embodiment shown, on the bottom wall 16 b of the supporting housing 16, by which means the first bottom wall 1 b is supported against the internal pressure. An intermediate layer 18, which is preferably made of a thermally insulating material, e.g. plastics material, is arranged between bottom walls 1 b and 16 b to reduce the heat withdrawn from digestion vessel 1.

[0028] Due to the relatively great length which is possible for it, the annular wall 7 c which extends downwards from screwing part 7 allows the screwing part 7 to have a relatively large range of adjustment and thus to be adapted to digestion vessels 1 of different heights, if the outside thread 7 b extends at least to the bottom end region of the annular wall 7 c or for example for its entire vertical length.

[0029] To prevent the pressure-applying plunger 6 from dropping out of the position where the screwing part 7 fits round it when there is no digestion vessel 1 under the device 5, a limiting arrangement 21 is provided between the pressure-applying plunger 6 and the screwing part 7, or rather the annular wall 7 c, to restrict the maximum extension movement of the pressure-applying plunger 6 and in the present embodiment this is formed by a stop arrangement having a stop member 22 in the region of the bottom end of annular wall 7 c. The opposing stop member is preferably formed by the sealing ring 13 a, which projects slightly from the circumferential surface of pressure-applying plunger 6 in the radial direction and can thus form the opposing stop member 22 without the need for any special opposing stop member. As a result, sealing ring 31 a performs a sealing and stopping function. Stop member 21 is formed by an internal annular bead on the inner circumferential surface of annular wall 7 c. To allow a small clearance for movement or sliding, the diameter of the annular bead is made larger than the diameter of pressure-applying plunger 6, thus enabling the latter to move in the annular bead. The inside diameter d2 of the annular bead is made somewhat larger than the inside diameter d1 of the rest of the annular wall 7 c, thus enabling the annular bead to be formed. At the same time, the inside diameter d2 is made only sufficiently large for sealing ring 13 a still to form a resilient seal against the inner circumferential surface 7 e of annular wall 7 c. In the present embodiment, the outer flank of the stop member 22 or annular bead is formed by an oblique or rounded lead-in face 23. The inner flank 24 is the face of a step which preferably extends approximately at right angles to the axis of the pressure-applying plunger 6. In the present embodiment the internal annular bead is pointed in cross-section, thus giving a pointed annular edge. This will cause the sealing ring 13 a to be sliced off if the pressure-applying plunger 6 is forcibly extracted from its socketed connection and protection is provided against dismantling in view of the damage that would be done to the sealing ring 13 a.

[0030] In the embodiment shown in FIG. 3, where the same or comparable parts have been given the same reference numerals, the screwing part 7 and its annular wall 7 c have been made so large that it fits round the digestion vessel 1 like a cap, at least in the region of the vessel's upper edge, and is screwed to the vessel so that the circumferential wall 1 a or the flange 1 c or a supporting shell 2 which is present if required, to any of which the annular wall 7 c may be screwed, forms the abutment 9. In the present embodiment a supporting ring 25 is fitted onto the digestion vessel 1, preferably in the top region of the digestion vessel 1, and in particular is arranged to rest against flange 1 c and to be connected to the outer circumferential surface of the digestion vessel 1, e.g. by pressing on or bonding. A connection of this kind ensures that the forces applied to the abutment are transmitted to the digestion vessel 1. If the supporting ring 25 rests against flange 1 c, there is no need for a connection to the outer circumferential surface as the flange 1 c supports the forces from the abutment. However, in this case too it is advantageous for the supporting ring 25 to be retained on the digestion vessel 1 in such a way that it cannot be lost, e.g. by pressing on or bonding.

[0031] The screwed connection between the screwing part 7 and the supporting ring 25 preferably comprises an inside thread 7 f in the region of the end of annular wall 7 c and a matching outside thread on the supporting ring 25.

[0032] In the two embodiments described above, the pressure-applying plunger 6 can form the cover 3, as shown in FIG. 3. In the embodiment shown in FIG. 1 the cross-sections of the pressure-applying plunger 6 and the screwing part 7 would have to be enlarged as appropriate to allow the pressure-applying plunger 6 to form the cover 3. The hole 14 would also have to end at a distance from that end of the pressure-applying plunger 6 which is adjacent the digestion vessel 1.

[0033] In all the embodiments it is also possible for the pressure-applying plunger 6 to be made U-shaped in cross-section as shown in FIG. 3 and for it thus to be provided with a circumferential wall 6d which, due to its axial length, ensures that the pressure-applying plunger 6 is guided in such a way as to be secure against tilting and which can also ensure that there is a sufficiently good seal. It is also advantageous for one or more grooves 6e spaced at an axial distance from one another to be arranged in the circumferential surface of the circumferential wall 6 d, these grooves both improving the seal and, in view of the differing thermal expansions, preventing any harmful stresses from arising in the fit, particularly when the material of the pressure-applying plunger is soft or yielding particularly at fairly high digestion temperatures.

[0034] In the embodiment shown in FIG. 3, the resilient pressure-generating means 8 is formed by a coil spring which is supported against the top wall of the screwing part 7 and engages against the pressure-applying plunger 6, in the bottom of a recess in the present case.

[0035] In the embodiment shown in FIG. 3 too, there may be provided a locating spigot 6 c which is once again preferably circular in cross-section and can be guided longitudinally or rather vertically in the top wall of the cap-like screwing part 7 with clearance for movement. At its bottom end the locating spigot 6 c preferably has a flange to reduce the pressure per unit area, against which the pressure-generating means 8 can bear.

[0036] In all the embodiments it is advantageous for there to be made, between the screwing part 7 and a part positioned on the digestion vessel 1 or the cover 3 or the pressure-applying plunger 6, a marking which shows the axial position of the screwing part 7 in relation to the part which is positioned and which preferably allows the screwing part 7 to be preset in a defined manner. The marking may for example be formed by a scale and a pointer which are situated on respective ones of the two parts to be compared. In the embodiment shown in FIG. 1 the marking 27 may be arranged for example on the top faces of the screwing part 7 and the abutment 9, preferably close to or at the threaded joint in the screwed assembly, e.g. in the form of an annular scale on the top wall 16 a and a pointer on the screwing part, 7.

[0037] In the embodiment shown in FIG. 3 the marking 27 may for example be formed by the front end of the locating spigot 6 c and the top or bottom edge of the guide hole 7 d. It is also possible for the markings or scale divisions to be made on the surface of the inner wall of the guide hole at axial distances from one another which, against the free end of the locating spigot 6 c, allow the position of the locating spigot 6 c, and hence the opened or closed position of the pressure-applying plunger 6 and if required of the cover too, to be seen or read off.

[0038] In the embodiment shown in FIG. 1 the digestion vessel 1 is made of a corrosion-resistant material and in particular of plastics material and preferably PTFE. The other parts of the digestion vessel 1 including the supporting housing 16 are preferably made of material which is permeable to microwaves and preferably plastics material. This may also be true of the device 5. In the embodiment shown, the spring or the resilient members forming the pressure-generating means 8 are made of metal and in particular of spring steel or stainless steel. The screwing part 7 too may be made of metal, e.g. stainless steel, in which case it acts as a Faraday cage for the spring. Operation is improved if the cage has a polished surface and its edges are rounded. It is also advantageous for the dimensions of the cage, i.e. its diameter and axial length, preferably to be sized at between a quarter and one complete wavelength of the microwave radiation used. In addition, the surface of the metal cage may be coated with a material, such as PTFE for example, which is resistant to corrosive chemicals, to prevent the surface of the metal from being attacked by such chemicals.

[0039] For a digestion process, a sample material is placed in the digestion vessel 1 and the digestion vessel 1 is closed with device 5. In the course of this the screwing part 7 is screwed in (FIG. 1) or on (FIG. 3) sufficiently far for the resilient pressure-generating means 8 to exert a closing force which corresponds to a given internal pressure. If the internal pressure rises in operation to more than a given value or rather the set value, the cover 3, i.e. the pressure-applying plunger 6, automatically opens, in which case the pressure-generating means 8 yields and the internal pressure can escape. This being the case, the device 5 acts as a pressure-release valve with the opening pressure being settable by screwing in the screwing part 7.

[0040] The embodiment shown in FIG. 3, where the same or comparable parts have been given the same reference numerals, differs from the embodiment described above in respect of a plurality of arrangements.

[0041] Firstly, the abutment 9 is not part of a supporting housing 16 which holds the entire digestion vessel 1 but of a small cap-like supporting housing 22 which, although it similarly transmits the reaction forces to the digestion vessel 1, only fits round the top region of the digestion vessel 1 and is supported directly or indirectly against this top region and thus transmits the reaction forces to this region of the digestion vessel 1. The direct or indirect connection to the top region of the digestion vessel 1 is made by a screwed connection. Provided in the annular wall 7 c above the flange 1 c or the supporting ring 25 is a radial venting opening 7 e. The bottom wall 1 b of the preferably cylindrical holding vessel 1 is preferably hemispherical in shape, thus enabling the wall to be evenly stressed. 

1. Device for closing a pot-like digestion vessel whose opening is covered by a cover, said device comprising: a pressure-applying plunger; a screwing part arranged co-axially with the pressure-applying plunger; and a resilient pressure-generating means arranged between the pressure-applying plunger and the screwing part, one of the screwing part and the pressure-applying plunger being fitted around the other in a socketed arrangement.
 2. Device according to claim 1, wherein an annular wall extends from the screwing part and fits around the pressure-applying plunger.
 3. Device according to claim 2, further including a ring seal arranged between the annular wall and the pressure applying plunger.
 4. Device according to claim 3, wherein the ring seal is formed by a sealing ring made of resilient material, said ring seal being mounted in at least one of an annular groove in the circumferential surface of the annular wall and the outer circumferential surface of the pressure applying plunger.
 5. Device according to claim 1, wherein the screwing part has an outside thread.
 6. Device according to claim 5, wherein the screwing part is screwed into a fixed abutment which is located above the screwing part and the pressure-applying plunger.
 7. Device for closing a pot-like digestion vessel whose opening is covered by a cover, said device comprising: a pressure-applying plunger; a screwing part which fits around the pressure-applying plunger, said screwing part having a screw thread in a bottom edge region thereof; and an abutment which surrounds the digestion vessel, said abutment being formed by a supporting ring which is fixed to a circumferential region of the digestion vessel.
 8. Device according to claim 2, wherein the supporting ring is fastenable to an outer circumferential surface of, fits under a flange of, or is formed on a flange of a digestion vessel.
 9. Device according to claim 7 or 8, wherein the pressure-applying plunger is guided to slide move axially along a hollow cylindrical slide face on the screwing part.
 10. Device according to claim 9, wherein axially spaced annular grooves are arranged in the cylindrical slide face of the pressure-applying plunger.
 11. Device according to claim 7, wherein the pressure-applying plunger is U-shaped in cross-section, and wherein a resilient pressure-generating means is arranged in a recess created by the U-shaped cross-section of the pressure-applying plunger.
 12. Device according to claim 11, wherein the resilient pressure-generating means is formed by disc or coil spring means.
 13. Device according to claim 7, wherein a co-axial hole is formed in the pressure-applying plunger.
 14. Device according to claim 7, wherein the screwing part has a guiding section in its top region for guiding an extension which extends from the pressure-applying plunger.
 15. Device according to claim 7, wherein the screwing apart is provided at its top with a formation for receiving a rotational force.
 16. Device according to claim 7, wherein the pressure-applying plunger forms a digestion vessel cover.
 17. Device according to claim 7, wherein, a position-indicating marking is arranged between the screwing part and the abutment. 